The present invention relates to a method for the detection of a line width of a line image in an image processor and, more particularly, to a method for the detection of a line width of a line image in an image processor, such as a computer-aided design apparatus for operating graphics, so adapted as to detect the line width of the line image as an object of tracing and to set a tracing rule for tracing the line image, when a line width of image data is traced in a semi-automatic way.
Heretofore, a general input method for entering a drawing written on paper into a graphic processing system involves entering the drawing as image data by the aid of an image scanner or the like, displaying the image data on a display screen through the graphic processing system, and entering the image data by tracing the image data displayed on the display screen with a pointing device or the like manually by an operator.
For instance, Japanese Patent Laid-open Publication (kokai) No. 62-269,276/1987 discloses a conversational graphic input system which comprises entering a drawing as image data into a computer by the aid of an image scanner, displaying the image data on a display screen so as to be superimposed on center line image data, and entering the graphics as vector data by designating necessary positions of the graphics on the display screen by the aid of a coordinate indicator.
When the image data are converted into, for example, graphic data such as vector data or the like, center data of the center (center line) of an image are given, data of necessary characteristic points, such as end points, branch points, corner points and so on, of the image are selected from the center line of the continuous center data, and the data therefor are designated and entered. In this case, the center data are displayed on the display screen so as to be superimposed on the image data in order to enter the characteristic point, thereby enabling an operator to easily determine the characteristic point and allowing the characteristic point to be entered by an input designation from the operator. This system, however, suffers from the disadvantage that items to be displayed on the display screen become so complex that the operator cannot select required data in an efficient fashion.
On the other hand, a graphic processing apparatus or system has been developed, which is provided with a semi-automatic image trace processing function so arranged as to trace an image point in a semi-automatic way, determine characteristic points and enter graphic data of the characteristic points in an image processor.
The semi-automatic image trace processing function of such an image processor allows a tracing rule, such as a line width of a line as the object of tracing and a method for the correction of a shape, to be set manually as a parameter.
It is noted, however, that when the trace processing is implemented for semi-automatically tracing the line image in the image data by the aid of the semi-automatic image trace processing function of the image processor, the operator sets a parameter for the line width of an image to be traced by estimating an approximate line width in the descriptive processing of the tracing rule of the semi-automatic image trace processing function, while looking at the line image displayed on the display screen of a display unit. In this case, however, the problem may arise that the line width of the line image is too difficult to determine with accuracy when the operator sets the line width thereof by eye estimation while looking at the image displayed on the display screen, because eye estimation of the image displayed on the display screen may vary with magnification at the time of displaying the image on the screen.